Solar collector systems for heating water have been utilized when the system includes a heat absorbing element in thermal contact with a heat carrier fluid which has a freezing point below that to which the collector may be subjected during winter time. The heat carrier fluid in such systems is pumped by a pump through a heat exchanger where the heat in the carrier fluid is transferred to water in turn circulated in a utility water circuit. Such systems are expensive to construct and operate, and their efficiency drops on increasing temperatures in comparison with those systems that circulate water directly in the absorber element and which do not use any separate heat exchanger. This is due in part to loss of heat in the heat exchanger unit itself.
Further conventional solar collectors having conventional metal absorber elements where water is circulated through the absorber element are subjected to deposits building up in the absorber element resulting from calcification of calcium containing water. Plastic absorber elements have been proposed to overcome the calcification problem but these have not been entirely satisfactory in that the plastic material loses its strength, particularly where parts are glued or welded together, due to high water temperatures. Further, such collectors in which water flows directly from the heat absorber element to the utility water circuit are subject to damage when the outside temperature drops below freezing due to water expanding on freezing.
It is therefore an object of my invention to provide for a solar collector in which water is heated by thermal contact with the absorber element of the collector and transferred directly to the utility water circuit without the intermediary of a separate heat exchanger, where the absorber element will not be subjected to unduly high temperatures, and which at the same time includes provision for preventing damage when the outside ambient temperature drops below the freezing point of water.